Methods of forming openings and methods of controlling the degree of taper of openings

ABSTRACT

Methods of forming contact openings and methods of controlling the degree of taper of contact openings are described. In one implementation, a layer is first etched through a contact mask opening using a first set of etching conditions. The etching conditions provide a first degree of sidewall taper from vertical, if etching completely through the layer. After the first etching, the layer is second etched through the contact mask opening using a second set of etching conditions. The second set of etching conditions provide a second degree of sidewall taper from vertical, if etching completely through the layer. The second degree of sidewall taper is different from the first degree of taper. In another embodiment, a material through which a contact opening is to be etched to a selected depth is formed over a substrate. A masking layer having an opening therein is formed over the material. The material is first etched through the opening with the first etch having a first selectivity relative to the masking layer. After the first etch, and at a depth which is less than about 50% of the selected depth, the material is second etched, with the second etch having a second selectivity relative to the masking layer which is greater than the first selectivity. In a preferred implementation, the second degree of selectivity is achieved by modifying an etch parameter during the etching of the contact opening.

TECHNICAL FIELD

This invention relates to methods of forming contact openings and tomethods of controlling the degree of taper of contact openings.

BACKGROUND OF THE INVENTION

When integrated circuitry is formed, contact openings are often formedthrough insulative material for establishing electrical communicationwith the integrated circuitry. Such contact openings are typicallysubsequently filled with conductive material, such as a metal orpolysilicon, whereby electrical communication is established with theintegrated circuitry.

Contact openings are often formed to be fairly narrow; and, it isdesirable from a design standpoint to form the contact openings to havesidewalls which are as near vertical as possible. This helps to ensurethat the contact area at the bottom of the contact opening issufficiently large to desirably cover and/or expose conductive materialwith which electrical communication is desired. As aspect ratios, i.e.the height-to-width ratio, of contact openings increase, it becomesincreasingly important to ensure that the dimension of the bottom of thecontact opening is sufficiently large to provide adequate coverage forconductive material which is subsequently formed therein. For narrowcontact openings, such is accomplished by maintaining the sidewalls ofthe contact opening as near vertical as possible. Referring to FIGS. 1and 2, two exemplary contact opening etch profiles are indicatedgenerally at 100, 100a respectively. FIG. 1 shows a substrate 102 with alayer of insulative material 104 formed thereover. A masking layer 106such as photoresist is formed over insulative material 104 and issubsequently patterned to define a contact opening pattern. Contactopening 108 is etched using an etch which is highly selective relativeto masking layer 106. Hence, while a desirably high level of selectivityensures that masking layer 106 remains over the substrate, thesubsequent etch profile is unsatisfactorily tapered. FIG. 2 shows asubstrate 100a in which like numbers from FIG. 1 have been utilized withthe suffix "a". There, a contact opening 108a is etched through layer104a using an etch with a comparatively lower degree of selectivityrelative to an overlying masking layer (not shown). The lower degree ofselectivity results in a contact opening profile with a more desirabledegree of taper. Yet, the overlying masking layer can be completelyremoved, thereby undesirably opening up other substrate features toetching.

This invention arose out of concerns associated with providing methodsof forming contact openings having sidewalls which are generallyvertical within desired tolerances. This invention also arose out ofconcerns associated with providing methods for controlling the degree oftaper of contact openings.

SUMMARY OF THE INVENTION

Methods of forming contact openings and methods of controlling thedegree of taper of contact openings are described. In oneimplementation, a layer is first etched through a contact mask openingusing a first set of etching conditions. The etching conditions providea first degree of sidewall taper from vertical, if etching completelythrough the layer. After the first etching, the layer is second etchedthrough the contact mask opening using a second set of etchingconditions. The second set of etching conditions provide a second degreeof sidewall taper from vertical, if etching completely through thelayer. The second degree of sidewall taper is different from the firstdegree of taper. In another embodiment, a material through which acontact opening is to be etched to a selected depth is formed over asubstrate. A masking layer having an opening therein is formed over thematerial. The material is first etched through the opening with thefirst etch having a first selectivity relative to the masking layer.After the first etch, and at a depth which is less than about 50% of theselected depth, the material is second etched, with the second etchhaving a second selectivity relative to the masking layer which isgreater than the first selectivity. In a preferred implementation, thesecond degree of selectivity is achieved by modifying an etch parameterduring the etching of the contact opening.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic side sectional view of a semiconductor waferfragment having a contact opening thereover which has been etchedutilizing an etch which is highly selective relative to an overlyingmasking layer.

FIG. 2 is a view which is similar to the FIG. 1 view, only one whichshows a contact opening which has been etched using an etch with a lowdegree of selectivity relative to a previously-formed masking layer.

FIG. 3 is a diagrammatic side sectional view of a semiconductor waferfragment in process in accordance with one aspect of the invention.

FIG. 4 is a view of the FIG. 3 wafer fragment at a different processingstep.

FIG. 5 is a view of the FIG. 3 wafer fragment at a different processingstep.

FIG. 6 is a view of a portion of a sidewall of a contact opening whichis etched in accordance with one aspect of the invention.

FIG. 7 is a graph which depicts taper angle versus step 1 etch depth.

FIG. 8 is a graph which depicts contact area versus step 1 etch depth.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

Referring to FIG. 3, a semiconductor wafer fragment in process is showngenerally at 10 and comprises a semiconductive substrate 12. In thecontext of this document, the term "semiconductive substrate" is definedto mean any construction comprising semiconductive material, including,but not limited to, bulk semiconductive materials such as asemiconductive wafer (either alone or in assemblies comprising othermaterials thereon), and semiconductive material layers (either alone orin assemblies comprising other materials). The term "substrate" refersto any supporting structure, including, but not limited to, thesemiconductive substrates described above.

In this example, substrate 12 has a diffusion region 13 formed thereinwith which electrical communication is desired. A layer 14 of materialis formed over substrate 12 and through which a contact opening having aselected depth is to be etched. An exemplary material for layer 14 is anoxide material such as borophosphosilicate glass (BPSG) formed to anexample thickness of 2.2 micron. In a preferred embodiment, layer 14comprises a single layer of BPSG. Other materials and numbers of layerscan, of course, be used. A masking layer 16 is formed over layer 14 andsubsequently patterned to define a contact mask opening 18 which exposesa surface portion 20 of layer 14. An exemplary material for maskinglayer 16 is photoresist.

Referring to FIG. 4, material of layer 14 is first etched throughcontact mask opening 18 using a first set of etching conditions orparameters which collectively provide a first degree of sidewall taperfrom vertical were etching to occur completely through the layer.

Referring to FIG. 5, and at an intermediate point proximate a first etchdepth, layer 14 is second etched using a second set of etchingconditions or parameters which provide a second degree of sidewall taperfrom vertical were etching to occur completely through the layer. Thesecond etching continues to proximate the depth selected for contactopening 22. In the illustrated example, the selected depth is one whichis sufficient to reach diffusion region 13. The second etching can,however, be terminated before reaching the ultimate depth to which thecontact opening is to be etched. Preferably, the second degree ofsidewall taper is different from the first degree of sidewall taper.Even more preferably, the first degree of sidewall taper is less thanthe second degree of sidewall taper.

Alternately considered, the first set of etching conditions are selectedto provide a first degree of selectivity relative to masking layer 16.At an etch depth which is less than about 50% of the selected depth ofthe desired contact opening, the etching conditions or parameters arechanged to provide the second etch with a second selectivity relative tomasking layer 16 which is greater than the first selectivity. In theillustrated and preferred embodiment, the first and second etches oflayer 14 are dry etches.

Referring to FIG. 6, a portion of a sidewall of contact opening 22 isindicated at 24. Such is displaced from a vertical line 25, or has adegree of taper from top-to-bottom away from vertical which defines anangle θ, wherein θ is preferably no greater than about 3°. Even morepreferably, θ is around 1.5°.

Referring to FIGS. 7 and 8, two graphs are set forth which describe datameasured in a reduction to practice example. In such example, a LAM TCP9100 high density oxide etcher was utilized to form contact openings asdescribed above. BPSG was utilized as the layer through which thecontact opening was etched, and the selected desired depth of thecontact opening was around 2 microns. In conducting the first etch ofthe BPSG, the following etch conditions or parameters were utilized:1050 Watts Source/1050 Watts Bias; 10 sccm C₂ HF₅, 15 sccm CHF₃, 5 sccmCH₂ F₂, at 15 mTorr. The first set of etch conditions comprise a firstratio of carbon to fluorine sufficient to provide a first degree ofselectivity relative to the masking layer, e.g. the photoresist. Thesecond etch was conducted with the following etch conditions orparameters: 700 Watts Source/700 Watts Bias; 20 sccm C₂ HF₅, 10 sccmCHF₃, 10 sccm CH₂ F₂ at 20 mTorr. The second set of etch conditionscomprise a second ratio of carbon to fluorine to provide a second degreeof selectivity relative to the masking layer which is different, andpreferably greater than the first degree of selectivity. Preferably, thesecond ratio is lower than the first ratio.

Table 1 below describes data associated with the first and secondetches. The first and second columns designated as "T1" and "T2"respectively, are the respective times, in seconds, of the first andsecond etches. The "Depth" column describes the depth, in microns, ofthe ultimately-etched contact opening, e.g. the selected depth. The "S1Depth" column describes the depth, in microns, at which the first etchwas modified to the second etch. The "Taper Angle" column describes theangle of taper of the sidewalls of the ultimately-etched contact openingaway from vertical.

Referring to FIG. 7, contact opening taper angle is plotted in degreesaway from vertical, as a function of the depth at which the first etchwas changed to the second etch. A plurality of data points are shown atA, B, C, D, E, F, and G. Each data point corresponds to an individualrow in Table 1. For example, data point G (last row in Table 1)describes a contact opening having a taper angle slightly larger than1.5°. Such contact opening was formed, referring to Table 1, byconducting the first etch for 30 seconds, modifying the etch chemistryor parameters, and then conducting the second etch for 150 seconds. Suchresulted in an intermediate switch point between etches of around 0.44micron, for a resulting contact opening depth of around 2.6 micron.

                  TABLE 1                                                         ______________________________________                                        T1             T2     Depth   S1 Depth                                                                             Taper Angle                              ______________________________________                                        (A)    1       150    2.3     0.015  3.005                                    (B)    5       145    2.2     0.073  2.434                                    (C)    10      140    2.3     0.147  2.434                                    (D)    15      135    2.3     0.220  2.148                                    (E)    20      130    2.3     0.293  2.005                                    (F)    40      110    2.2     0.587  2.148                                    (G)    30      150    2.6     0.440  1.575                                    ______________________________________                                    

Referring to FIG. 8, contact area at the bottom of the contact openingis plotted as a function of the depth at which the first etch waschanged to the second etch for the same data points. Utilizing the sameparameters or etch conditions as described above in connection with FIG.7, the largest contact area observed appeared where the degree of taperaway from vertical was the smallest, i.e. data point G. Such isdesirable, as mentioned above, from the standpoint of opening up as muchpotential conductive contact area within desired tolerances.

Accordingly, methods of the present invention enable a degree of contactopening taper to be controlled and selected. Such methods also providefor contact openings having generally vertical sidewalls which increasethe contact area at the bottom of the contact opening.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A method of forming an opening through a layer ofmaterial comprising:providing a layer of a material; first etching intothe material through a mask opening using a first set of etchingconditions which are defined by a first degree of sidewall taper fromvertical, the first etching forming an opening in the material; afterthe first etching, second etching into the material through the maskopening using a second set of etching conditions which are defined by asecond degree of sidewall taper from vertical, the second degree ofsidewall taper being different from the first degree of taper; thesecond etching extending the opening downwardly into the material; andwherein the first degree of sidewall taper is less than the seconddegree of sidewall taper.
 2. A method of forming an opening in a layerof material comprising:providing a layer of a material; first etchinginto the material through a mask opening using a first set of etchingconditions which are defined by a first degree of sidewall taper fromvertical, the first etching forming an opening in the material; afterthe first etching, second etching into the material through the maskopening using a second set of etching conditions which are defined by asecond degree of sidewall taper from vertical, the second degree ofsidewall taper being different from the first degree of taper; thesecond etching extending the opening downwardly into the material; thefirst degree of sidewall taper is less than the second degree ofsidewall taper; and the first and second etchings have different degreesof selectivity relative to material from which the mask is formed.